lnd.xprv/chainntnfs/btcdnotify/btcd.go

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package btcdnotify
import (
"errors"
"fmt"
"sync"
"sync/atomic"
"time"
"github.com/lightningnetwork/lnd/chainntnfs"
"github.com/roasbeef/btcd/btcjson"
"github.com/roasbeef/btcd/chaincfg/chainhash"
"github.com/roasbeef/btcd/rpcclient"
"github.com/roasbeef/btcd/wire"
"github.com/roasbeef/btcutil"
)
const (
// notifierType uniquely identifies this concrete implementation of the
// ChainNotifier interface.
notifierType = "btcd"
// reorgSafetyLimit is assumed maximum depth of a chain reorganization.
// After this many confirmation, transaction confirmation info will be
// pruned.
reorgSafetyLimit = 100
)
var (
// ErrChainNotifierShuttingDown is used when we are trying to
// measure a spend notification when notifier is already stopped.
ErrChainNotifierShuttingDown = errors.New("chainntnfs: system interrupt " +
"while attempting to register for spend notification.")
)
// chainUpdate encapsulates an update to the current main chain. This struct is
// used as an element within an unbounded queue in order to avoid blocking the
// main rpc dispatch rule.
type chainUpdate struct {
blockHash *chainhash.Hash
blockHeight int32
// connected is true if this update is a new block and false if it is a
// disconnected block.
connect bool
}
// txUpdate encapsulates a transaction related notification sent from btcd to
// the registered RPC client. This struct is used as an element within an
// unbounded queue in order to avoid blocking the main rpc dispatch rule.
type txUpdate struct {
tx *btcutil.Tx
details *btcjson.BlockDetails
}
// TODO(roasbeef): generalize struct below:
// * move chans to config, allow outside callers to handle send conditions
// BtcdNotifier implements the ChainNotifier interface using btcd's websockets
// notifications. Multiple concurrent clients are supported. All notifications
// are achieved via non-blocking sends on client channels.
type BtcdNotifier struct {
spendClientCounter uint64 // To be used atomically.
epochClientCounter uint64 // To be used atomically.
started int32 // To be used atomically.
stopped int32 // To be used atomically.
chainConn *rpcclient.Client
notificationCancels chan interface{}
notificationRegistry chan interface{}
spendNotifications map[wire.OutPoint]map[uint64]*spendNotification
txConfNotifier *chainntnfs.TxConfNotifier
blockEpochClients map[uint64]*blockEpochRegistration
chainUpdates *chainntnfs.ConcurrentQueue
txUpdates *chainntnfs.ConcurrentQueue
wg sync.WaitGroup
quit chan struct{}
}
// Ensure BtcdNotifier implements the ChainNotifier interface at compile time.
var _ chainntnfs.ChainNotifier = (*BtcdNotifier)(nil)
// New returns a new BtcdNotifier instance. This function assumes the btcd node
// detailed in the passed configuration is already running, and willing to
// accept new websockets clients.
func New(config *rpcclient.ConnConfig) (*BtcdNotifier, error) {
notifier := &BtcdNotifier{
notificationCancels: make(chan interface{}),
notificationRegistry: make(chan interface{}),
blockEpochClients: make(map[uint64]*blockEpochRegistration),
spendNotifications: make(map[wire.OutPoint]map[uint64]*spendNotification),
chainUpdates: chainntnfs.NewConcurrentQueue(10),
txUpdates: chainntnfs.NewConcurrentQueue(10),
quit: make(chan struct{}),
}
ntfnCallbacks := &rpcclient.NotificationHandlers{
OnBlockConnected: notifier.onBlockConnected,
OnBlockDisconnected: notifier.onBlockDisconnected,
OnRedeemingTx: notifier.onRedeemingTx,
}
// Disable connecting to btcd within the rpcclient.New method. We
// defer establishing the connection to our .Start() method.
config.DisableConnectOnNew = true
config.DisableAutoReconnect = false
chainConn, err := rpcclient.New(config, ntfnCallbacks)
if err != nil {
return nil, err
}
notifier.chainConn = chainConn
return notifier, nil
}
// Start connects to the running btcd node over websockets, registers for block
// notifications, and finally launches all related helper goroutines.
func (b *BtcdNotifier) Start() error {
// Already started?
if atomic.AddInt32(&b.started, 1) != 1 {
return nil
}
// Connect to btcd, and register for notifications on connected, and
// disconnected blocks.
if err := b.chainConn.Connect(20); err != nil {
return err
}
if err := b.chainConn.NotifyBlocks(); err != nil {
return err
}
_, currentHeight, err := b.chainConn.GetBestBlock()
if err != nil {
return err
}
b.txConfNotifier = chainntnfs.NewTxConfNotifier(
uint32(currentHeight), reorgSafetyLimit)
b.chainUpdates.Start()
b.txUpdates.Start()
b.wg.Add(1)
go b.notificationDispatcher(currentHeight)
return nil
}
// Stop shutsdown the BtcdNotifier.
func (b *BtcdNotifier) Stop() error {
// Already shutting down?
if atomic.AddInt32(&b.stopped, 1) != 1 {
return nil
}
// Shutdown the rpc client, this gracefully disconnects from btcd, and
// cleans up all related resources.
b.chainConn.Shutdown()
close(b.quit)
b.wg.Wait()
b.chainUpdates.Stop()
b.txUpdates.Stop()
// Notify all pending clients of our shutdown by closing the related
// notification channels.
for _, spendClients := range b.spendNotifications {
for _, spendClient := range spendClients {
close(spendClient.spendChan)
}
}
for _, epochClient := range b.blockEpochClients {
close(epochClient.cancelChan)
epochClient.wg.Wait()
close(epochClient.epochChan)
}
b.txConfNotifier.TearDown()
return nil
}
// onBlockConnected implements on OnBlockConnected callback for rpcclient.
// Ingesting a block updates the wallet's internal utxo state based on the
// outputs created and destroyed within each block.
func (b *BtcdNotifier) onBlockConnected(hash *chainhash.Hash, height int32, t time.Time) {
// Append this new chain update to the end of the queue of new chain
// updates.
b.chainUpdates.ChanIn() <- &chainUpdate{
blockHash: hash,
blockHeight: height,
connect: true,
}
}
// filteredBlock represents a new block which has been connected to the main
// chain. The slice of transactions will only be populated if the block
// includes a transaction that confirmed one of our watched txids, or spends
// one of the outputs currently being watched.
// TODO(halseth): this is currently used for complete blocks. Change to use
// onFilteredBlockConnected and onFilteredBlockDisconnected, making it easier
// to unify with the Neutrino implementation.
type filteredBlock struct {
hash chainhash.Hash
height uint32
txns []*btcutil.Tx
// connected is true if this update is a new block and false if it is a
// disconnected block.
connect bool
}
// onBlockDisconnected implements on OnBlockDisconnected callback for rpcclient.
func (b *BtcdNotifier) onBlockDisconnected(hash *chainhash.Hash, height int32, t time.Time) {
// Append this new chain update to the end of the queue of new chain
// updates.
b.chainUpdates.ChanIn() <- &chainUpdate{
blockHash: hash,
blockHeight: height,
connect: false,
}
}
// onRedeemingTx implements on OnRedeemingTx callback for rpcclient.
func (b *BtcdNotifier) onRedeemingTx(tx *btcutil.Tx, details *btcjson.BlockDetails) {
// Append this new transaction update to the end of the queue of new
// chain updates.
b.txUpdates.ChanIn() <- &txUpdate{tx, details}
}
// notificationDispatcher is the primary goroutine which handles client
// notification registrations, as well as notification dispatches.
func (b *BtcdNotifier) notificationDispatcher(currentHeight int32) {
out:
for {
select {
case cancelMsg := <-b.notificationCancels:
switch msg := cancelMsg.(type) {
case *spendCancel:
chainntnfs.Log.Infof("Cancelling spend "+
"notification for out_point=%v, "+
"spend_id=%v", msg.op, msg.spendID)
// Before we attempt to close the spendChan,
// ensure that the notification hasn't already
// yet been dispatched.
if outPointClients, ok := b.spendNotifications[msg.op]; ok {
close(outPointClients[msg.spendID].spendChan)
delete(b.spendNotifications[msg.op], msg.spendID)
}
case *epochCancel:
chainntnfs.Log.Infof("Cancelling epoch "+
"notification, epoch_id=%v", msg.epochID)
// First, we'll lookup the original
// registration in order to stop the active
// queue goroutine.
reg := b.blockEpochClients[msg.epochID]
reg.epochQueue.Stop()
// Next, close the cancel channel for this
// specific client, and wait for the client to
// exit.
close(b.blockEpochClients[msg.epochID].cancelChan)
b.blockEpochClients[msg.epochID].wg.Wait()
// Once the client has exited, we can then
// safely close the channel used to send epoch
// notifications, in order to notify any
// listeners that the intent has been
// cancelled.
close(b.blockEpochClients[msg.epochID].epochChan)
delete(b.blockEpochClients, msg.epochID)
}
case registerMsg := <-b.notificationRegistry:
switch msg := registerMsg.(type) {
case *spendNotification:
chainntnfs.Log.Infof("New spend subscription: "+
"utxo=%v", msg.targetOutpoint)
op := *msg.targetOutpoint
if _, ok := b.spendNotifications[op]; !ok {
b.spendNotifications[op] = make(map[uint64]*spendNotification)
}
b.spendNotifications[op][msg.spendID] = msg
case *confirmationNotification:
chainntnfs.Log.Infof("New confirmation "+
"subscription: txid=%v, numconfs=%v",
msg.TxID, msg.NumConfirmations)
// Lookup whether the transaction is already included in the
// active chain.
txConf, err := b.historicalConfDetails(
msg.TxID, msg.heightHint, uint32(currentHeight),
)
if err != nil {
chainntnfs.Log.Error(err)
}
err = b.txConfNotifier.Register(&msg.ConfNtfn, txConf)
if err != nil {
chainntnfs.Log.Error(err)
}
case *blockEpochRegistration:
chainntnfs.Log.Infof("New block epoch subscription")
b.blockEpochClients[msg.epochID] = msg
}
case item := <-b.chainUpdates.ChanOut():
update := item.(*chainUpdate)
if update.connect {
if update.blockHeight != currentHeight+1 {
chainntnfs.Log.Warnf("Received blocks out of order: "+
"current height=%d, new height=%d",
currentHeight, update.blockHeight)
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continue
}
currentHeight = update.blockHeight
rawBlock, err := b.chainConn.GetBlock(update.blockHash)
if err != nil {
chainntnfs.Log.Errorf("Unable to get block: %v", err)
continue
}
chainntnfs.Log.Infof("New block: height=%v, sha=%v",
update.blockHeight, update.blockHash)
txns := btcutil.NewBlock(rawBlock).Transactions()
block := &filteredBlock{
hash: *update.blockHash,
height: uint32(update.blockHeight),
txns: txns,
connect: true,
}
if err := b.handleBlockConnected(block); err != nil {
chainntnfs.Log.Error(err)
}
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continue
}
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if update.blockHeight != currentHeight {
chainntnfs.Log.Warnf("Received blocks out of order: "+
"current height=%d, disconnected height=%d",
currentHeight, update.blockHeight)
continue
}
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currentHeight = update.blockHeight - 1
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chainntnfs.Log.Infof("Block disconnected from main chain: "+
"height=%v, sha=%v", update.blockHeight, update.blockHash)
err := b.txConfNotifier.DisconnectTip(uint32(update.blockHeight))
if err != nil {
chainntnfs.Log.Error(err)
}
// NOTE: we currently only use txUpdates for mempool spends and
// rescan spends. It might get removed entirely in the future.
case item := <-b.txUpdates.ChanOut():
newSpend := item.(*txUpdate)
spendingTx := newSpend.tx
// First, check if this transaction spends an output
// that has an existing spend notification for it.
for i, txIn := range spendingTx.MsgTx().TxIn {
prevOut := txIn.PreviousOutPoint
// If this transaction indeed does spend an
// output which we have a registered
// notification for, then create a spend
// summary, finally sending off the details to
// the notification subscriber.
if clients, ok := b.spendNotifications[prevOut]; ok {
spenderSha := newSpend.tx.Hash()
spendDetails := &chainntnfs.SpendDetail{
SpentOutPoint: &prevOut,
SpenderTxHash: spenderSha,
SpendingTx: spendingTx.MsgTx(),
SpenderInputIndex: uint32(i),
}
// TODO(roasbeef): after change to
// loadfilter, only notify on block
// inclusion?
confirmedSpend := false
if newSpend.details != nil {
confirmedSpend = true
spendDetails.SpendingHeight = newSpend.details.Height
} else {
spendDetails.SpendingHeight = currentHeight + 1
}
// Keep spendNotifications that are
// waiting for a confirmation around.
// They will be notified when we find
// the spend within a block.
rem := make(map[uint64]*spendNotification)
for c, ntfn := range clients {
// If this is a mempool spend,
// and this client didn't want
// to be notified on mempool
// spends, store it for later.
if !confirmedSpend && !ntfn.mempool {
rem[c] = ntfn
continue
}
confStr := "unconfirmed"
if confirmedSpend {
confStr = "confirmed"
}
chainntnfs.Log.Infof("Dispatching %s "+
"spend notification for "+
"outpoint=%v at height %v",
confStr, ntfn.targetOutpoint,
spendDetails.SpendingHeight)
ntfn.spendChan <- spendDetails
// Close spendChan to ensure that any calls to Cancel will not
// block. This is safe to do since the channel is buffered, and the
// message can still be read by the receiver.
close(ntfn.spendChan)
}
delete(b.spendNotifications, prevOut)
// If we had any clients left, add them
// back to the map.
if len(rem) > 0 {
b.spendNotifications[prevOut] = rem
}
}
}
case <-b.quit:
break out
}
}
b.wg.Done()
}
// historicalConfDetails looks up whether a transaction is already included in a
// block in the active chain and, if so, returns details about the confirmation.
func (b *BtcdNotifier) historicalConfDetails(txid *chainhash.Hash,
heightHint, currentHeight uint32) (*chainntnfs.TxConfirmation, error) {
// First, we'll attempt to retrieve the transaction details using the
// backend node's transaction index.
txConf, err := b.confDetailsFromTxIndex(txid)
if err != nil {
return nil, err
}
if txConf != nil {
return txConf, nil
}
// If the backend node's transaction index is not enabled, then we'll
// fall back to manually scanning the chain's blocks, looking for the
// block where the transaction was included in.
return b.confDetailsManually(txid, heightHint, currentHeight)
}
// confDetailsFromTxIndex looks up whether a transaction is already included
// in a block in the active chain by using the backend node's transaction index.
// If the transaction is found, its confirmation details are returned.
// Otherwise, nil is returned.
func (b *BtcdNotifier) confDetailsFromTxIndex(txid *chainhash.Hash,
) (*chainntnfs.TxConfirmation, error) {
// If the transaction has some or all of its confirmations required,
// then we may be able to dispatch it immediately.
tx, err := b.chainConn.GetRawTransactionVerbose(txid)
if err != nil {
// Avoid returning an error if the transaction index is not
// enabled to proceed with fallback methods.
jsonErr, ok := err.(*btcjson.RPCError)
if !ok || jsonErr.Code != btcjson.ErrRPCNoTxInfo {
return nil, fmt.Errorf("unable to query for txid "+
"%v: %v", txid, err)
}
}
// Make sure we actually retrieved a transaction that is included in a
// block. Without this, we won't be able to retrieve its confirmation
// details.
if tx == nil || tx.BlockHash == "" {
return nil, nil
}
// As we need to fully populate the returned TxConfirmation struct,
// grab the block in which the transaction was confirmed so we can
// locate its exact index within the block.
blockHash, err := chainhash.NewHashFromStr(tx.BlockHash)
if err != nil {
return nil, fmt.Errorf("unable to get block hash %v for "+
"historical dispatch: %v", tx.BlockHash, err)
}
block, err := b.chainConn.GetBlockVerbose(blockHash)
if err != nil {
return nil, fmt.Errorf("unable to get block with hash %v for "+
"historical dispatch: %v", blockHash, err)
}
// If the block was obtained, locate the transaction's index within the
// block so we can give the subscriber full confirmation details.
targetTxidStr := txid.String()
for txIndex, txHash := range block.Tx {
if txHash == targetTxidStr {
return &chainntnfs.TxConfirmation{
BlockHash: blockHash,
BlockHeight: uint32(block.Height),
TxIndex: uint32(txIndex),
}, nil
}
}
// We return an error because we should have found the transaction
// within the block, but didn't.
return nil, fmt.Errorf("unable to locate tx %v in block %v", txid,
blockHash)
}
// confDetailsManually looks up whether a transaction is already included in a
// block in the active chain by scanning the chain's blocks, starting from the
// earliest height the transaction could have been included in, to the current
// height in the chain. If the transaction is found, its confirmation details
// are returned. Otherwise, nil is returned.
func (b *BtcdNotifier) confDetailsManually(txid *chainhash.Hash,
heightHint, currentHeight uint32) (*chainntnfs.TxConfirmation, error) {
targetTxidStr := txid.String()
// Begin scanning blocks at every height to determine where the
// transaction was included in.
for height := heightHint; height <= currentHeight; height++ {
blockHash, err := b.chainConn.GetBlockHash(int64(height))
if err != nil {
return nil, fmt.Errorf("unable to get hash from block "+
"with height %d", height)
}
// TODO: fetch the neutrino filters instead.
block, err := b.chainConn.GetBlockVerbose(blockHash)
if err != nil {
return nil, fmt.Errorf("unable to get block with hash "+
"%v: %v", blockHash, err)
}
for txIndex, txHash := range block.Tx {
// If we're able to find the transaction in this block,
// return its confirmation details.
if txHash == targetTxidStr {
return &chainntnfs.TxConfirmation{
BlockHash: blockHash,
BlockHeight: height,
TxIndex: uint32(txIndex),
}, nil
}
}
}
// If we reach here, then we were not able to find the transaction
// within a block, so we avoid returning an error.
return nil, nil
}
// handleBlocksConnected applies a chain update for a new block. Any watched
// transactions included this block will processed to either send notifications
// now or after numConfirmations confs.
// TODO(halseth): this is reusing the neutrino notifier implementation, unify
// them.
func (b *BtcdNotifier) handleBlockConnected(newBlock *filteredBlock) error {
// First we'll notify any subscribed clients of the block.
b.notifyBlockEpochs(int32(newBlock.height), &newBlock.hash)
// Next, we'll scan over the list of relevant transactions and possibly
// dispatch notifications for confirmations and spends.
for _, tx := range newBlock.txns {
mtx := tx.MsgTx()
txSha := mtx.TxHash()
for i, txIn := range mtx.TxIn {
prevOut := txIn.PreviousOutPoint
// If this transaction indeed does spend an output which we have a
// registered notification for, then create a spend summary, finally
// sending off the details to the notification subscriber.
clients, ok := b.spendNotifications[prevOut]
if !ok {
continue
}
// TODO(roasbeef): many integration tests expect spend to be
// notified within the mempool.
spendDetails := &chainntnfs.SpendDetail{
SpentOutPoint: &prevOut,
SpenderTxHash: &txSha,
SpendingTx: mtx,
SpenderInputIndex: uint32(i),
SpendingHeight: int32(newBlock.height),
}
for _, ntfn := range clients {
chainntnfs.Log.Infof("Dispatching spend notification for "+
"outpoint=%v", ntfn.targetOutpoint)
ntfn.spendChan <- spendDetails
// Close spendChan to ensure that any calls to Cancel will not
// block. This is safe to do since the channel is buffered, and
// the message can still be read by the receiver.
close(ntfn.spendChan)
}
delete(b.spendNotifications, prevOut)
}
}
// A new block has been connected to the main chain.
// Send out any N confirmation notifications which may
// have been triggered by this new block.
b.txConfNotifier.ConnectTip(&newBlock.hash, newBlock.height, newBlock.txns)
return nil
}
// notifyBlockEpochs notifies all registered block epoch clients of the newly
// connected block to the main chain.
func (b *BtcdNotifier) notifyBlockEpochs(newHeight int32, newSha *chainhash.Hash) {
epoch := &chainntnfs.BlockEpoch{
Height: newHeight,
Hash: newSha,
}
for _, epochClient := range b.blockEpochClients {
select {
case epochClient.epochQueue.ChanIn() <- epoch:
case <-epochClient.cancelChan:
case <-b.quit:
}
}
}
// spendNotification couples a target outpoint along with the channel used for
// notifications once a spend of the outpoint has been detected.
type spendNotification struct {
targetOutpoint *wire.OutPoint
spendChan chan *chainntnfs.SpendDetail
spendID uint64
mempool bool
heightHint uint32
}
// spendCancel is a message sent to the BtcdNotifier when a client wishes to
// cancel an outstanding spend notification that has yet to be dispatched.
type spendCancel struct {
// op is the target outpoint of the notification to be cancelled.
op wire.OutPoint
// spendID the ID of the notification to cancel.
spendID uint64
}
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// RegisterSpendNtfn registers an intent to be notified once the target
// outpoint has been spent by a transaction on-chain. Once a spend of the target
// outpoint has been detected, the details of the spending event will be sent
// across the 'Spend' channel. The heightHint should represent the earliest
// height in the chain where the transaction could have been spent in.
func (b *BtcdNotifier) RegisterSpendNtfn(outpoint *wire.OutPoint,
heightHint uint32, mempool bool) (*chainntnfs.SpendEvent, error) {
ntfn := &spendNotification{
targetOutpoint: outpoint,
spendChan: make(chan *chainntnfs.SpendDetail, 1),
spendID: atomic.AddUint64(&b.spendClientCounter, 1),
heightHint: heightHint,
mempool: mempool,
}
select {
case <-b.quit:
return nil, ErrChainNotifierShuttingDown
case b.notificationRegistry <- ntfn:
}
if err := b.chainConn.NotifySpent([]*wire.OutPoint{outpoint}); err != nil {
return nil, err
}
// The following conditional checks to ensure that when a spend
// notification is registered, the output hasn't already been spent. If
// the output is no longer in the UTXO set, the chain will be rescanned
// from the point where the output was added. The rescan will dispatch
// the notification.
txOut, err := b.chainConn.GetTxOut(&outpoint.Hash, outpoint.Index, true)
if err != nil {
return nil, err
}
if txOut == nil {
// First, we'll attempt to retrieve the transaction's block hash
// using the backend's transaction index.
tx, err := b.chainConn.GetRawTransactionVerbose(&outpoint.Hash)
if err != nil {
// Avoid returning an error if the transaction was not
// found to proceed with fallback methods.
jsonErr, ok := err.(*btcjson.RPCError)
if !ok || jsonErr.Code != btcjson.ErrRPCNoTxInfo {
return nil, fmt.Errorf("unable to query for "+
"txid %v: %v", outpoint.Hash, err)
}
}
var blockHash *chainhash.Hash
if tx != nil && tx.BlockHash != "" {
// If we're able to retrieve a valid block hash from the
// transaction, then we'll use it as our rescan starting
// point.
blockHash, err = chainhash.NewHashFromStr(tx.BlockHash)
if err != nil {
return nil, err
}
} else {
// Otherwise, we'll attempt to retrieve the hash for the
// block at the heightHint.
blockHash, err = b.chainConn.GetBlockHash(
int64(heightHint),
)
if err != nil {
return nil, err
}
}
// We'll only request a rescan if the transaction has actually
// been included within a block. Otherwise, we'll encounter an
// error when scanning for blocks. This can happen in the case
// of a race condition, wherein the output itself is unspent,
// and only arrives in the mempool after the getxout call.
if blockHash != nil {
ops := []*wire.OutPoint{outpoint}
err = b.chainConn.Rescan(blockHash, nil, ops)
if err != nil {
chainntnfs.Log.Errorf("Rescan for spend "+
"notification txout failed: %v", err)
return nil, err
}
}
}
return &chainntnfs.SpendEvent{
Spend: ntfn.spendChan,
Cancel: func() {
cancel := &spendCancel{
op: *outpoint,
spendID: ntfn.spendID,
}
// Submit spend cancellation to notification dispatcher.
select {
case b.notificationCancels <- cancel:
// Cancellation is being handled, drain the spend chan until it is
// closed before yielding to the caller.
for {
select {
case _, ok := <-ntfn.spendChan:
if !ok {
return
}
case <-b.quit:
return
}
}
case <-b.quit:
}
},
}, nil
}
// confirmationNotification represents a client's intent to receive a
// notification once the target txid reaches numConfirmations confirmations.
type confirmationNotification struct {
chainntnfs.ConfNtfn
heightHint uint32
}
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// RegisterConfirmationsNtfn registers a notification with BtcdNotifier
// which will be triggered once the txid reaches numConfs number of
// confirmations.
func (b *BtcdNotifier) RegisterConfirmationsNtfn(txid *chainhash.Hash,
numConfs, heightHint uint32) (*chainntnfs.ConfirmationEvent, error) {
ntfn := &confirmationNotification{
ConfNtfn: chainntnfs.ConfNtfn{
TxID: txid,
NumConfirmations: numConfs,
Event: chainntnfs.NewConfirmationEvent(numConfs),
},
heightHint: heightHint,
}
select {
case <-b.quit:
return nil, ErrChainNotifierShuttingDown
case b.notificationRegistry <- ntfn:
return ntfn.Event, nil
}
}
// blockEpochRegistration represents a client's intent to receive a
// notification with each newly connected block.
type blockEpochRegistration struct {
epochID uint64
epochChan chan *chainntnfs.BlockEpoch
epochQueue *chainntnfs.ConcurrentQueue
cancelChan chan struct{}
wg sync.WaitGroup
}
// epochCancel is a message sent to the BtcdNotifier when a client wishes to
// cancel an outstanding epoch notification that has yet to be dispatched.
type epochCancel struct {
epochID uint64
}
// RegisterBlockEpochNtfn returns a BlockEpochEvent which subscribes the
// caller to receive notifications, of each new block connected to the main
// chain.
func (b *BtcdNotifier) RegisterBlockEpochNtfn() (*chainntnfs.BlockEpochEvent, error) {
reg := &blockEpochRegistration{
epochQueue: chainntnfs.NewConcurrentQueue(20),
epochChan: make(chan *chainntnfs.BlockEpoch, 20),
cancelChan: make(chan struct{}),
epochID: atomic.AddUint64(&b.epochClientCounter, 1),
}
reg.epochQueue.Start()
// Before we send the request to the main goroutine, we'll launch a new
// goroutine to proxy items added to our queue to the client itself.
// This ensures that all notifications are received *in order*.
reg.wg.Add(1)
go func() {
defer reg.wg.Done()
for {
select {
case ntfn := <-reg.epochQueue.ChanOut():
blockNtfn := ntfn.(*chainntnfs.BlockEpoch)
select {
case reg.epochChan <- blockNtfn:
case <-reg.cancelChan:
return
case <-b.quit:
return
}
case <-reg.cancelChan:
return
case <-b.quit:
return
}
}
}()
select {
case <-b.quit:
// As we're exiting before the registration could be sent,
// we'll stop the queue now ourselves.
reg.epochQueue.Stop()
return nil, errors.New("chainntnfs: system interrupt while " +
"attempting to register for block epoch notification.")
case b.notificationRegistry <- reg:
return &chainntnfs.BlockEpochEvent{
Epochs: reg.epochChan,
Cancel: func() {
cancel := &epochCancel{
epochID: reg.epochID,
}
// Submit epoch cancellation to notification dispatcher.
select {
case b.notificationCancels <- cancel:
// Cancellation is being handled, drain
// the epoch channel until it is closed
// before yielding to caller.
for {
select {
case _, ok := <-reg.epochChan:
if !ok {
return
}
case <-b.quit:
return
}
}
case <-b.quit:
}
},
}, nil
}
}